The present invention relates to an operative temperature sensing system and, more particularly, to such a system that accurately, simply and inexpensively senses (for indication and/or control purposes) the operative temperature which closely approximates the thermal environmental sensing capabilities of a human being.
As used herein the term "operative temperature" is qualitatively defined as: "the uniform temperature of a radiantly black enclosure in which an occupant would exchange the same amount of heat by radiation plus convection as in the actual nonuniform environment". Quantitatively "operative temperature" is the average, weighted by respective heat transfer coefficients, of the air and mean radiant temperatures, or: EQU T.sub.o =(H.sub.c T.sub.a +H.sub.r T.sub.r)/(H.sub.c +H.sub.r)
wherein:
T.sub.o =operative temperature PA0 T.sub.a =air or ambient temperature PA0 T.sub.r =mean radiant temperature PA0 H.sub.c =convective heat transfer coefficient PA0 H.sub.r =radiative heat transfer coefficient.
The prior art is replete with proposed devices which sense factors which purport to correlate human or animal comfort levels with such sensed variables; however, none appear to sense operative temperature (as defined above) in a simple inexpensive and accurate system.
Among such prior art are the following prior U.S. Patents:
1. U.S. Pat. No. 2,685,795--relates to a panradiometer consisting of four spheres of differing emmissivities to thereby detect total environmental radiation by heat balancing techniques.
2. U.S. Pat. No. 2,739,204--relates to a space thermostat wherein a single ambient temperature sensor is exposed so as to be sensitive to heat radiating from radiators within the space to be heated.
3. U.S. Pat. No. 3,062,941--relates to a radiation sensitive infrared control for animal heating wherein a globular sensing unit, containing an electrical heating element and a thermistor, is employed to control the infrared source in response to variations in ambient temperature within the globe.
4. U.S. Pat. No. 3,092,997--relates to a heat sensing device wherein a single thermistor is housed within a dome and is shielded from sunlight such that the heat of radiation is transferred at a relatively uniform rate thereto.
5. U.S. Pat. No. 3,246,838--relates to controls for infrared emitters wherein a thermostatic element is provided with a heater for artificially raising the temperature of the surface of the element to approximate the temperature at the surface of the human body.
6. U.S. Pat. No. 3,531,991--relates to a mean radiation temperature meter employing at least three radiation sensing elements having different thermal emmissivity characteristics.
7. U.S. Pat. No. 4,058,254--relates to a temperature monitoring and control system wherein the surface of the sensing means has a radiant absorbtion coefficient which corresponds to that of a human being whereby the output signal therefrom is used to control the occupied space so that the surface of the sensing means is maintained constant in an attempt to maintain thermal comfort.
8. U.S. Pat. No. 4,073,190--relates to a cold stress meter wherein a measurement is obtained that takes into account the effects on body heat loss, of sun, wind and air temperature. A bead transistor is responsive to both ambient temperature and wind. Other means are provided that are representative of the nonevaporative rate of body heat loss, thermal insulation resistance of still air outside of clothing, fraction of full sunlight intensity reaching a person wearing clothing and the absorbtance of the clothing.
9. U.S. Pat. No. 4,123,939--relates to a device for sensing total thermal energy received by an object in a given location wherein thermocouples are placed within a sphere to provide a signal indicative of the thermal energy gradients within the sphere.
10. U.S. Pat. No. 4,164,869--relates to a thermostat for radiant room heating wherein a thin film sensor is used in a bridge network to provide an error signal to actuate a heater.